Wire-wound resistance and method of making same



Se pt. 24, 1946. PATTERSON 2,408,092

WIRE-WOUND RESISTANCE AND METHOD OF MAKING SAME Filed Jan. 30, 1943 3 Sheets-Sheet 1 WWW/#211111 INVENTOR By EM. PATTERSON AT TORNEV Sept. 24, 1946. E. M. PATTERSON 2,408,092

Filed Jan. 30', 1943 s Sheets-Sheet 2 a a; I l I v do I .29 I

ATTORNEY Patented Sept. 24, 1946 WIRE-WOUND RESISTANCE AND METHOD OF MAKING SAME Everett M. Patterson, Waterbury,

Conn., assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application January 30, 1943, Serial No. 474,129

1 Claim. 1

This invention relates to wire-wound resistance devices and more particularly to resistance devices in which a card-type support is wound with resistance wire.

The object of the invention is to provide a wirewound resistance in which the turns of wire will remain in required positions on the cardtype support.

A feature of the invention resides in the structure of the card-type support.

Another feature resides in a modification of the card-type support in which a thread is provided along an edge portion of the support.

The card-type supports in this invention are grooved at required points to receive the turns of resistance wire and the groove extend at least part way over edge portions of the card-type support. The grooves are formed in the cardtype support by placing a suitably formed and constructed card between grooved plates and by pressing the plates against the card. The method of making the card-type supports is claimed in my copending application Serial No. 519,462, filed January 24, 1944, as a division of the present application.

In the drawings:

Figs. 1, 2 and 3 show three steps in making a grooved plate to be used in pressure forming grooves in the card-type support;

Fig. 4 shows one of the grooved plates in perspective;

Fig. 5 shows an advanced step in forming the plate;

Fig. 6 is a view in perspective of a press with two of the grooved plates mounted in the press;

Fig. 7 is a view in perspective of a piece of sheet material from which a card-type support is to be cut;

Fig. 8 is a view in perspective of one form of card cut from the sheet shown in Fig. '7

Fig. 9 is an nd view of the press shown in Fig. 6 and with a card located between two plates mounted in the press and after the plates have been pressed against the card;

Fig. 10 is an enlarged cross-sectional view of portions of Fig. 9;

Fig. 11 is a plan view of one form of card-type support constructed in accordance with the invention and partly wound with resistance wire;

Fig. 12 is a cross-sectional view of a portion of the resistance device and taken on the line lZ-IZ in Fig. 11;

Fig. 13 is a plan view of a modification of the resistance device structure; and

Fig. 14 is a cross-sectional view of a portion of 2 the device shown in Fig. 13 and taken on the line I4l4. I

In making electrical resistance devices comprising a card-type insulating support and a resistance wire wound helically on the support it is found necessary in some cases to maintain the turns of the resistance wire accurately spaced from each other. It has been found quite difficult to maintain the correct spacing of the turns of wire when the card-type support does not have parallel long edge portions and when at least one of the long edge portions is contoured to provide a rather steep curve. The difiiculty is overcome in some cases by winding the wire under such tension that the Wire will dig into edge portions of the support. In other cases where close spacing of the turns of wire is not necessary notches have been cut in the edge portion of the support and the wire is guided into these notches during th winding operation. These procedures have their limitations, however, since in the first case overtensioning the wire might break the wire or change its resistance value and in the second case hand cutting notches to very close space limits is tedious, expensive and, in most cases, not sufiiciently accurate and machine tools operable to accurately cut notches across an edge portion of a card at, say notches per inch, and suitable for cutting notches in cards of considerable length to such close limits are not readily available.

In the present invention the card-type support is provided with thermoplastic flat surfaces and these surfaces are molded to provide required grooves in the card-type support and some of the thermoplastic material is extruded beyond the original edge portions of the card-type support and retains parts of the groove pattern impressed on the card-type support.

When a wir is wound on the card-typ support the portions of the wire extending over the edge portions of the card-type support are located in the grooves in the extruded portions of the thermoplastic material and the wire is thus prevented from slipping along the length of the card-type support.

To obtain the required groove pattern and provide means for forming the pattern on a card type support a cylinder [5 of impressionable material as shown in Fig. l is rotated against a cutting tool l6 so that a required groove pattern will be cut in the outer cylindrical surface of the cylinder 15, the cutting tool It being moved lengthwise of the cylinder l5 under'the action of a lead screw or other suitable tool feeding means, not

a shown, and the cylinder it; being supported at opposite ends by means of supports l! and I8, one at least of which is in driving engagement with the cylinder l and rotated by a suitable driving m ans, not shown. The cylinder [5 should be made of such material that a helical groove l9 may be readily cut in the outer surface by means of th tool it. I have used, for instance, lead as the material for the cylinder l5 since the helical groove it may be readily cut in this material. It will be assumed merely for the purpose of explaining the invention that the cylinder it is made of lead and the groove l9 extends from one end of the cylinder it to the other.

After the groove has been formed a metal coating is applied to the outer surface of the cylinder iii as shown in Fig. 2. The coating 2|! may be applied, for instance, by electroplating the cyiinder is with copper or other suitable metal, inner surface of the coating 2i taking in reverse form the pattern of the groove on the cylinder i d the metal coating it being sufiiciently t to have no groove pattern on the outer surface.

The coating 213 is cut longitudinally as shown at in Fig. 3 and is peeled off the cylinder it as shown in this figure is then flattened out to make a fiat plate 23 shown in Fig. 4, the plate having the groove pattern M on the upper surface having a plain ungrooved lower surface The plate is mounted on a thicker backing plate at; as shown in Fig, 5, the plain under sur face oi": the plate 23 being secured to the backing plat-c it in any suitable manner so that the plates 2? and 26 form a relatively thick plate 21, one surface of which contains the groove pattern it .An exact duplicate 23 i formed of the plate 21 and the two plates 2'5 and 23 are mounted in a press shown in Fig. 6, the press 29 having two men 1g plates and iii which may be heated in any suitable manner. It will be obvious that the mounting plates it and iii may be electrically heated by heating means extending into the apertures 32 or that steam or other heat supplying pipes may be connected to the mounting plates and 3t through the apertures 32 in order that the mounting plates 30 and El! may be heated to a required temperature. The press 29 is constructed and arranged so that the mounting plates and ill ma be brought closer together. suitable press for the purpose is a hydraulic press in which the mounting plate 3! is supported on a hydraulically operated piston 33, the mounting plate 38 is fixed and guide rods 34 for the mounting plates are supported on the mounting plate and xtended through apertures provided ing plate It is obvious that if a sheet of thermoplastic material is placed between the groove patterned plate 2'! and 28 mounted in the press and the press is operated to move the plates 2'? and 28 against opposite faces of the thermoplastic sheet while the mounting plates 3i) and El are heated to a sufficient temperature to bring the groove patterned plates 21 and 28 to a temperature suh'icient to soften the thermoplastic sheet, the upper lower surfaces of the thermoplastic sheet will be molded to the groove pattern impressed therein by the plates 2! and 23. By applying sufficient heat and pressure to the thermoplastic sheet through operation of the press 29 some of the thermoplastic material may be made to extrude beyond the original edges of the thermoplastic sheet. The thermoplastic material and the temperature imparted to it should be such that the groove pattern will remain in the extruded portions of the material extended over the original long edge portions of the sheet. A suitable thermoplastic material for the purpose is cellulose acetate. It is obvious, however, that other thermoplastic materials may be used instead of cellulose acetate and that the invention is not limited to he use of cellulose acetate. It will be assumed, however, merely for the purpose of explaining the invention that such material is used in the construction of the card-type support.

Fig. '7 shows a sheet 35 comprising an inner layer 38 coated on opposite face 31 with thermoplastic material which may be cellulose acetate or other suitable thermoplastic material.

From the sheet 35 a card is cut of desired form such, for instance, as the card 38 shown in Fig. 8. This card has a long straight edge portion 39 and curved edge portion so and after being impressed with the groove pattern of the plates 2'! and 28 in the press 29 will become a card-type support on which resistance wire may be wound, the turns of wire being guided into and being held in grooves formed, in the pressing operation, on the edge portions 39 and iii, the grooves provided to prevent the wire from slipping along the long edge portions of the card-type support.

To make a card-type support having the required groove pattern the card 38 is placed between the plates 27 and 28 in the press 29, the plates 2'5 and 2.8 are heated to a suiiicient temperature to soften the thermoplastic coatings and the press 29 is operated to squeeze the plates 21 and 28 against the thermoplastic surfaces on the card 38. The temperature should be only suflicient to soften the thermoplastic material and not high enough to make the material run freely.

As shown in Figs. 9 and 10, a card-type support M has been made from the card 38 in the man-- ner above described. It will be seen b looking at these figures that some of the thermoplastic material has been extruded as indicated at lk-G3 beyond the original edge portions 39 and 40 of the card, that the extruded portions t2 and 43 turn inwardly toward each other on each edge portion of the card-type support M and that the groove pattern continues in the extruded portions 42 and 43. as indicated at M, in the extruded portion 42 shown in Fig. ll). The extruded portions 42 and 43 are, in efiect, spaced ridges extending along the edges of the card-type support, the ridges cooperating to form a channel along each long edge of the card-type support.

When a 'wire 45 is wound on the card-type support 4! as shown in Fig. ii, the portions of the wire 45 extended around the long edge portions of the card-type support M rest the grooves 44 in the extruded portions and "it so that the turns of the wire are held in reouired spaced relation and are prevented from slipping along the long edge portions of the car .type support M. This is of particular advantage in mak n a so-called tapered resistance when the r. ulrcd taper is obtained by winding the wire on a ,apered form card-type support having a relativ y steep curve along one of its edge portions. wire cannot slide down the curved edge potion of the card-type support.

I have made card-type supports by the method above described and have found that even when the edge portions are formed to provide relatively steep curves the turns of wire wound on the cardtype support will remain in their required positions. Also that the turns of wire will remain in their required positions on the card-type support when the wire-wound card is bent into the form of a ring suitable for forming part of a potentiometer in which the resistance unit is a ring type support wound with wire and a wiper contact is rotated over and in contact with an edge portion of the wire-wound resistance unit.

Since the thermoplastic material is on opposite faces of the card-type support and some of the thermoplastic material is extruded. so that portions overhang the original long edge portions of the support the sheet 35 from which the cardtype support is cut may be a laminated structure in which the inner layer 36 is made of either metal or sheet insulating material. In some cases I may make the card-type support entirely of thermoplastic material and control the heat and pressure applied by the press 29 so that the outer flat surfaces will be softened and molded by means of the p1ates 2? and. 28 to the required groove pattern and there will be some of the outer surface material extruded beyond the original long edge portions of the card and the groove pattern will be continued into the extruded portions.

In the modifi ation shown in Figs. 13 and 14 the card-type support 45 is made in the same manner as the card-type support 4! above described. In modification, however, each long edge portion of the card-type support 45 is provided with an impressionable insulating thread. The threads ll and 48 may be made of cellulose acetate or other insulating material sufficiently soft at norrnal room temperature to allow the wire 45 to partly sink into the thread when the wire 45 is wound on the card-type support. The thread 41 is laid in a channel 49 resulting along the curved edge of the card-type support 6 when the extruded portions 42 and 43 are formed, the channel 49 being defined by the original curved edge of the card and the extruded portions 42 and of thermoplastic material.

The thread 43 is laid in a channel 53 resulting along the long straight edge or the card-type support 46 when the extruded portions 42 and #3 are formed, the channel 59 being defined by the original long straight edge of the card and the extruded portions 42 and 43 of thermoplastic material. The thread 5| shown in Fig. 13 is, in effect. a continuation of the thread 41 and is provided at the point indicated when the card-type support 46 is made in the general form shown and is abruptly widened on an end portion of the structure.

When the wire 45 is wound on the card-type support 46 the wire 45 binds the threads il, and 5| into the channels formed by the extruded portions 42 and 43 along edge portions of the card-type support. The diameter of the threads 47, 48 and 5| is slightly greater than the depth of the channels and the threads are indented under the tension of the wire 45, the indentations made in the thread being, in effect, continuations of the groove pattern formed in the extruded portions 42 and 43, one of the grooves of which is illustrated at 44 in Fig. 10.

It will be seen, as illustrated in Figs. 13 and 14., that the grooves formed in the extruded portions 32 and 43 of the thermoplastic material and the indentations made in the threads 41 and 48 will prevent the turns of wire 45 from slipping along the card-type support 46.

The Wire-wound resistance formed in accord ance with this invention may be mounted on a suitable support in a resistance device in which a wiper contact is provided to successively engage the turns of resistance wire. card may be bent into the form of a ring and mounted on an annular support and the wiper contact may be arranged to operate over and in contact with the turns of wire extending over the long straight edge portion or" the resistance. In the case of the structure shown in Figs. 13 and 14 the thread 48 will provide a backing for the turns of resistance wire where the wire is engaged by the wiper contact and prevent undue distortion and displacement of the turns of the resistance wire by the action of the wiper contact.

What is claimed is:

A wire-Wound electrical resistance device comprising a card-type support, surfaces of thermoplastic material on opposite faces of said support and formed to provide spaced ridges along edge portions of said support, a pattern of grooves formed in said surfaces and continued into said ridges, a wire helically wound on said support and having portions extending into the groove pattern in said ridges, a thread located between said ridges and extending along an edge of said support, said thread being indented by portions of said wire extending over edge portions of said support and said thread cooperating with the grooves in said ridges to prevent said wire from slipping along said support and said thread also serving as a backing for portions of said wire extending from one of said ridges to the other.

EVERETT M. PATTERSON.

The wire-wound. 

